1. Field of the Invention
The present invention relates generally to elevated support structures, and more particularly to a support pole for raising and lowering an object between an elevated position and a lower position.
2. Description of Related Art
It is often desirable to support an object in an elevated position. For example, surveillance cameras, lights, signs, flags, banners, antennas and weather monitoring equipment are often supported a distance above the ground by mounting on a pole or mast. The added height can provide considerable advantage, including improved visibility, a better vantage point, improved signal reception, and avoidance of interference by lower structures and objects. However, maintenance, repair and installation of elevated equipment is often difficult and expensive, and may expose personnel to additional risk of injury due to the possibility of falls. Often, special equipment such as ladders, scaffolding or bucket trucks are required for access to elevated equipment.
Efforts have been made to facilitate service of elevated equipment at ground level by providing masts having equipment that can be raised and lowered. For example, U.S. Pat. No. 4,051,525 to Kelly, and U.S. Pat. No. 5,975,726 to Latimer disclose poles having cable lift mechanisms for raising and lowering equipment. Previously known poles facilitating the raising and lowering of equipment, however, have not proven fully satisfactory for a variety of reasons. For example, the lift mechanisms of such poles are often quite complex and include a substantial number of moving parts, rendering them expensive to produce and maintain. In addition, many such mechanisms incorporate external working parts such as pulleys and cables, which are exposed to damage from the elements, present a risk of injury to persons coming into contact with moving parts, and detract considerably from the external aesthetic appeal of the overall device. Also, the lift mechanisms of many such poles require specialized tools and equipment to operate and service, and often require a dedicated power source to drive the lift mechanism, adding further to the expense and complexity of the device.
U.S. Pat. No. 6,447,150 discloses a support pole for raising and lowering equipment, and is incorporated herein by reference. This support pole provides a cable transport mechanism for carrying an electrical cable connected to the equipment mounted on a carriage as the carriage is raised and lowered. A plug and socket arrangement allows the cable to be manually connected and disconnected from a power source, surveillance equipment, and/or other associated equipment. International Publication WO 01/75849 A2, also incorporated herein by reference, discloses another form of cable transport mechanism, wherein the cables are carried by pulleys. U.S. patent application Publication No. US-2003-0024144-A1, also incorporated herein by reference, discloses another support pole having similar means of cable transport.
Although such devices provide considerable advantage over previously known elevated support structures, it has now been discovered to be desirable to eliminate the need for transporting the cable with the carriage as it is raised and lowered, and to enable isolation of high-voltage cables from low-voltage cables in a support pole. It is to the provision of a pole and lifting device meeting these and other needs that the present invention is primarily directed.